I''ll start by saying that I am not familiar with these engines........but a cam seal seems like a likely curprit, but dont rule out that it could just be oil from when the rocker cover was leaking that was never cleaned up. You have done the right thing by degreasing and cleaning it all up and just keep an eye on it for the next few weeks.
Looking at your photos the oil leak does not look fresh which leads me to think its possibly left over from when the rocker cover gasket was leaking.
Not sure when the timing belt was last replaced, but seeing its been exposed to oil for a period of time it might be a good idea to get it replaced soonish once you sort out the leak.
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